A mobile COVID-19 vaccination and booster shot site operates out of a bus on 59th Street south of Central Park as patients wait on the sidewalk, Thursday, Dec. 2, 2021, in New York. (AP Photo/John Minchillo)

The omicron variant of COVID-19, which had been undetected in the U.S. before the middle of this week, had been discovered in at least five states by the end of Thursday, showing yet again how mutations of the virus can circumnavigate the globe with speed and ease.

Just a day after the first known U.S. case was found in California, tests showed the omicron variant had infected at least five people in the New York City metropolitan area, plus a man from Minnesota who had attended an anime convention in Manhattan in late November.

A Colorado woman who had recently traveled to southern Africa, a Hawaii resident with no recent travel history, and another California resident who traveled to South Africa last month also were infected by the variant, officials said.

Much remains unknown about omicron, including whether it is more contagious, as some health authorities suspect, whether it can thwart vaccines and whether it makes people as sick as the original strain.

Health officials in each state said there was no cause for undue alarm. But the spread of the cases, some involving people who hadn’t been away from home recently, meant the variant was likely already circulating domestically in some parts of the U.S.

"We gotta assume there’s a lot more behind that and that it has been here for a meaningful amount of time," New York City Mayor Bill de Blasio said at a news conference with Gov. Kathy Hochul.

The infected New Yorkers included a 67-year-old woman on Long Island who had recently traveled to South Africa, residents of Brooklyn and Queens and another case possibly linked to travel. At least one person had received a dose of a COVID-19 vaccine but officials did not have details about the vaccination status of the four other cases.

In Minnesota, health officials said a man who had not traveled outside the U.S. began experiencing symptoms the day after attending the Anime NYC 2021 convention in New York City. Minnesota Health Commissioner Jan Malcolm said it’s likely the man contracted COVID-19 at the convention, but officials did not know for sure.

Officials in New York said they were working to trace attendees of the convention, which was held Nov. 19-21 and drew about 50,000 people, according to event organizers. Attendees were required to wear masks and show proof of having received at least one dose of a COVID-19 vaccine.

It was held at the Jacob K. Javits Convention Center as New York City prepared to host the annual Macy’s Thanksgiving Day Parade and braced for throngs of tourists to return after the U.S. opened up to vaccinated international travelers.

City Health Commissioner Dave Chokshi urged people who attended the event to get tested.

"This is not just due to people who are traveling to southern Africa or to other parts of the world where omicron has already been identified," Chokshi said Thursday.

The Minnesota man began experiencing mild symptoms Nov. 22. He had been vaccinated and received a booster shot in early November, according to health officials in his home state. He sought COVID-19 testing Nov. 24, and his symptoms have subsided, officials said.

Nov. 22 was the same day the person infected in the first California case returned to the U.S. from South Africa. The California traveler, who was vaccinated, developed mild symptoms and tested positive Monday. The second person in the state didn’t need medical care and was also vaccinated.

The unvaccinated adult infected with the variant in Hawaii had gotten COVID-19 a year ago. The person isn’t currently hospitalized and had "mild-to-moderate" symptoms including headache, body aches and cough, Hawaii Epidemiologist Dr. Sarah Kemble said.

She wouldn’t identify the patient other to say the person lives on the island of Oahu.

Omicron is classified by the World Health Organization as a "variant of concern" as scientists work to determine how it may compare with the predominant delta variant in terms of transmissibility and severity. Scientists also are studying the degree to which existing vaccines and therapies protect against omicron.

Scientists in South Africa first reported it, but the samples came from several countries in southern Africa. And health officials in the Netherlands now say it was found there prior to the South Africa detection.

As comfort over air travel returns, it’s inevitable that new variants like omicron will spread from country to country and state to state, said professor Danielle Ompad, an epidemiologist at New York University’s School of Global Public Health.

"We shouldn’t panic, but we should be concerned," she said.

Hochul said the case involving the Minnesota visitor underlined the need for everyone who is eligible to get vaccinated against COVID-19 or receive a booster shot if they have not already."

There is one way to address this — New Yorkers, get vaccinated, get boosted, and get ready," the Democrat said.

The Associated Press contributed to this report.

Dr. Anthony Fauci, right, director of the National Institute of Allergy and Infectious Diseases, speaks as Dr. Rochelle Walensky, Director of the Centers for Disease Control and Prevention (CDC), looks on during a Senate Health, Education, Labor, and Pensions Committee hearing on Capitol Hill, Thursday, Nov. 4, 2021, in Washington. (AP Photo/Alex Brandon)

Speaking at the White House COVID-19 Response Team press briefing, U.S. Centers for Disease Control and Prevention (CDC) Director Dr. Rochelle Walensky said Friday that the omicron COVID-19 variant has been identified in approximately 40 countries around the world.

The public health leader said the agency is working with state and local public health authorities to investigate suspect cases.

The variant of concern has been located in California, Minnesota, New York, Colorado and Hawaii so far.

"Across the country, public health departments are looking at sequence data and travel histories and epidemiological indicators and diagnostic data to identify possible cases of omicron," she said.

"We are equipped and prepared to fight the omicron variant head on," Walensky added later, instructing that Americans get boosted against the virus "right away."

Following the director's remarks, America's top infectious disease expert Dr. Anthony Fauci told reporters that more will be known about omicron in coming days and weeks.

White House COVID-19 Response Coordinator Jeffrey Zients said that the variant is "a cause for concern, not panic."

He said the U.S. has the tools and the know-how in order to be able to keep people safe.

"Join your fellow Americans, who are rolling up their sleeves," Zients urged.

A traveler arrives to enter into a COVID-19 testing center at the Incheon International Airport In Incheon, South Korea, Wednesday, Dec. 1, 2021. South Korea's daily jump in coronavirus infections exceeded 5,000 for the first time since the start of the pandemic, as a delta-driven surge also pushed hospitalizations and deaths to record highs. (AP Photo/Ahn Young-joon)

Measures used to counter the delta variant should remain the foundation for fighting the coronavirus pandemic, even in the face of the new omicron version of the virus, World Health Organization officials said Friday, while acknowledging that the travel restrictions imposed by some countries may buy time.

While about three dozen countries worldwide have reported omicron infections, including India on Thursday, the numbers so far are small outside of South Africa, which is facing a rapid rise in COVID-19 cases and where the new variant may be becoming dominant. Still, much remains unclear about omicron, including whether it is more contagious, as some health authorities suspect, whether it makes people more seriously ill, or whether it can evade vaccine protection.

“Border control can delay the virus coming in and buy time. But every country and every community must prepare for new surges in cases,” Dr. Takeshi Kasai, the WHO regional director for the Western Pacific, told reporters Friday during a virtual news conference from the Philippines. “The positive news in all of this is that none of the information we have currently about omicron suggests we need to change the directions of our response.”

That means continuing to push for higher vaccination rates, abiding by social-distancing guidelines, and wearing masks, among other measures, said WHO Regional Emergency Director Dr. Babatunde Olowokure.

He added that health systems must “ensure we are treating the right patients in the right place at the right time, and so therefore ensuring that ICU beds are available, particularly for those who need them.”

Kasai warned: “We cannot be complacent.”

WHO has previously urged against border closures, noting they often have limited effect and can cause major disruptions. Officials in southern Africa, where the omicron variant was first identified, have decried restrictions on travelers from the region, saying they are being punished for alerting the world to the mutant strain.

Scientists are working furiously to learn more about omicron, which has been designated a variant of concern because of the number of mutations and because early information suggests it may be more transmissible than other variants, Kasai said.

A few countries in Western Pacific region are facing surges that began before omicron was identified, though COVID-19 cases and deaths in many others have decreased or plateaued, Kasai said. But that could change.

Among the places that have found the variant in the region are Australia, Hong Kong, Japan, South Korea, Singapore and Malaysia — and it is likely to crop up in more places.

The emergence of omicron is of particular concern for organizers of the Beijing Winter Olympic Games, now about two months away.

Beijing is adopting a series of measures to reduce the risk the virus will spread during the Games, Zhao Weidong, spokesperson for the organizing committee, told reporters at a briefing on Friday.

China has adopted a zero-tolerance policy toward COVID-19 transmission and has some of the world’s strictest border controls. Games participants will have to live and compete inside a bubble, and only spectators who are residents of China and have been vaccinated and tested will be permitted at venues.

Globally, cases have been increasing for seven consecutive weeks and the number of deaths has started to rise again, too, driven largely by the delta variant and decreased use of protective measures in other parts of the world, Kasai said.

“We should not be surprised to see more surges in the future. As long as transmission continues, the virus can continue to mutate, as the emergence of omicron demonstrates, reminding us of the need to stay vigilant,” Kasai said.

He warned especially about the likelihood of surges due to more gatherings and movement of people during the holiday season. The northern winter season will also likely bring other infectious respiratory diseases, such as the flu, alongside COVID-19.

“It is clear that this pandemic is far from over and I know that people are worried about omicron,” Kasai said. “But my message today is that we can adapt the way we manage this virus to better cope with the future surges and reduce their health, social and economic impacts.”

The Associated Press contributed to this report.

LeBron James is arguably one of the top three basketball players of all time and has one of the smartest basketball IQs of anyone who has ever stepped onto the floor.

On Thursday night, there was something that perplexed the Los Angeles Lakers superstar as he geared up to return to NBA action following a COVID scare of his own. He couldn’t understand why players on his son Bronny’s high school basketball team were wearing face masks under their chins instead of over their noses and mouths.

"I’m sorry but I’m at my boys game and the mask underneath the chin makes ZERO sense to me!!" James tweeted.

Click here to read more on Fox News.

Dr. Anthony Fauci will be a guest on Fox Business' "Cavuto: Coast to Coast" with Neil Cavuto at 1 p.m. ET. to dicuss the pandemic.

As the U.S. and the world begins to focus on the newly identified omicron variant of the coronavirus, the delta variant is continuing to spread.

A hospital in St. Cloud Minnesota has been completely full with patients for nearly two months, the Washington Post reported.

“We just continue to see rail car after rail car pile onto this derailment,” coronavirus response incident commander George Morris, who works for the hospital's parent organization, said of delta. “Omicron is potentially another train coming."

Eric Topol, the director of the Scripps Research Translational Institute, said to "forget" about omicron for the moment.

“We are not even handling delta well, no matter what happens to omicron. We have the combination of elapsed time, a hyper-contagious variant and relaxed mitigation. It’s the perfect storm to have a surge," he said.

The omicron variant of the coronavirus has been documented in the New York City area.

Five cases of the variant have been confirmed in New York City, Mayor Bill de Blasio and Gov. Kathy Hochul said on Thursday evening. 

"New York State has confirmed five cases of the omicron variant," Hochul tweeted. "Let me be clear: This is not cause for alarm. We knew this variant was coming and we have the tools to stop the spread. Get your vaccine. Get your booster. Wear your mask."

Click here to read more on Fox News.